1. Field of the Invention
The present invention relates to a battery testing device and a battery testing method for testing a chargeable secondary battery by applying a load, by performing charging using a charging means to charge the secondary battery and discharging of this secondary battery.
2. Related Background Art
As a multimedia function (e.g. transmission/reception of mail and viewing TV) of portable telephones, there is a format to use a portable telephone while simultaneously being recharged by connecting a charger (that is, and AC adapter) as shown in FIG. 1 in order to enable lengthy use of the portable telephone. FIG. 1 is a block diagram depicting a state when an AC adapter 91 is connected to a portable telephone 90. The AC adapter 91 is also connected to a commercial power supply 99. A portable telephone 90 encloses a lithium ion battery 92 as a secondary battery pack, a charge control circuit 93, and a radio circuit 94 as a load device to discharge the battery, in many cases.
A tendency of a lithium ion battery 92 enclosed in many electronic equipment, including portable telephones 90, which occurs depending on the state of use of the electronic equipment (e.g. charging frequency, number of times of use, ambient temperature during uses) is that the battery capacity decreases (that is capacity deterioration of the battery) or the thermal stability of the materials inside the battery (that is active materials) drops, the thermo-runaway easily occurs when the temperature inside the battery becomes high.
For example, in a case of using a portable telephone 90 while being charged by being connected to an AC adapter, as mentioned above, charge and discharge are repeated in a highly charged state where the voltage is in about a 4.0 V to 4.2 V range, as shown in FIG. 2, so the charge amount required for a 100% chargeable amount gradually decreases, and the capacity deterioration of the lithium ion battery 92 as the secondary battery progresses. FIG. 2 is a graph showing an example of the change of battery voltage when charge and discharge are repeated in the lithium ion battery 92 being connected for charging. In the case of using [the equipment] while being connected for charging like this, when charging completes, the power required for activating the above mentioned radio circuit 94 is discharged from the above mentioned radio circuit is discharged from the lithium ion battery 92 to the radio circuit 94. As a result, battery voltage drops, and charge is restarted when [the battery voltage] reaches the recharge start voltage Vstart (e.g. about 4.0 V in FIG. 2), and this cycle is repeated.
Conventionally a test to evaluate the performance of the secondary battery, such as the degree of the above mentioned capacity deterioration of a secondary battery, a complete discharge (that is a 100% discharge) of the secondary battery and a complete charge (that is a 100% charge) are regarded as one cycle, and a test to evaluate the performance of the secondary battery is performed by repeating this cycle. This battery performance test is performed by using a test device disclosed in Japanese Patent Application Laid-Open No. H8-136600, for example.
However in this conventional battery performance test, the actual case of using a portable telephone while being charged by being connected to an AC adapter, as mentioned above, is not considered, therefore a better result than actual performance is exhibited in this conventional battery performance test, and the performance of the secondary battery cannot be evaluated accurately.